Extensible nonwoven fabric and composite nonwoven fabric comprising the same

ABSTRACT

An extensible nonwoven fabric comprises a fiber comprising at least two olefin-based polymers. These olefin-based polymers are of the same kind and have different induction periods of strain-induced crystallization as measured at the same temperature and shear strain rate. A composite nonwoven fabric of the invention comprises at least one layer comprising the extensible nonwoven fabric.

TECHNICAL FIELD

The present invention relates to an extensible nonwoven fabric. Moreparticularly, the invention relates to an extensible nonwoven fabricwhich is capable of extension during mechanical stretching, hasexcellent fuzz resistance, surface abrasion resistance, formability andproductivity, and can be heat-embossed at low temperatures. Theinvention also relates to a composite nonwoven fabric produced bylaminating the nonwoven fabric and to a disposable diaper comprising thenonwoven fabric.

BACKGROUND OF THE INVENTION

Nonwoven fabrics have wide applications including clothes, disposablediapers and personal hygiene products. The nonwoven fabrics for suchapplications are required to have excellent properties, such as touch,conformability to the body, conformity during body movements, drape,tensile strength and surface abrasion resistance.

Traditional nonwoven fabrics made from a monocomponent fiber, whilebeing resistant to fuzzing and comfortable to the touch, areunsatisfactory in extensibility. Accordingly, there has been adifficulty in using such nonwoven fabrics in diapers and the like whereboth comfortable touch and good extensibility are required.

It has been believed that the nonwoven fabrics are desirably impartedwith elastic properties in order to meet the above requirements, andvarious methods have been proposed for imparting elastic properties. Forexample, mechanical stretching of composite nonwoven fabrics thatinclude at least one elastic layer and at least one substantiallyinelastic layer can produce elastic properties. However, the compositenonwoven fabrics by this method have problems in that the inelasticfiber is damaged or broken during the mechanical stretching to producefuzz and the fabric strength is lowered.

In consideration of such problems, studies have been being carried outin order to impart high extensibility to the inelastic fibers. Forexample, JP-A-9/512313 and WO 01/49905 propose composite nonwovenfabrics that comprise multipolymer fibers containing two or moredifferent polymers as the inelastic fibers. The multipolymer fiberscontained in the composite nonwoven fabrics have achieved highextensibility. However, the composite nonwoven fabrics according to theteachings of these publications suffer fuzzing and have inferior touch.

OBJECT OF THE INVENTION

It is an object of the present invention to provide an extensiblenonwoven fabric which is excellent in strength, extensibility, fuzzresistance, surface abrasion resistance, formability and productivityand which can be heat-embossed at low temperatures. It is another objectof the invention to provide a composite nonwoven fabric produced bylaminating the extensible nonwoven fabric.

DISCLOSURE OF THE INVENTION

The present inventors earnestly studied with a view to solving theaforesaid problems. As a result, they have found that a fiber thatcomprises olefin-based polymers of the same kind having differentinduction periods of strain-induced crystallization at the sametemperature can exhibit high extensibility. The present invention hasbeen completed based on this finding.

The extensible nonwoven fabric according to the invention comprises afiber comprising at least two olefin-based polymers, these at least twoolefin-based polymers being of the same kind and having differentinduction periods of strain-induced crystallization as measured at thesame temperature and the same shear strain rate.

Preferably, the fiber is a conjugate fiber having a cross section inwhich a component in point (a) and a component in point (b) which issymmetric about the center point are the same.

Preferably, the extensible nonwoven fabric is a spunbonded nonwovenfabric.

Preferably, the extensible nonwoven fabric has an extensibility at amaximum load of not less than 70% in the machine direction (MD) and/orin the cross machine direction (CD).

Preferably, the olefin-based polymer is a propylene-based polymer.

The composite nonwoven fabric according to the invention comprises atleast one layer comprising the extensible nonwoven fabric as describedabove. The disposable diaper of the invention includes the extensiblenonwoven fabric as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing changes in melt shear viscosity measured inthe invention with time;

FIG. 2 is a sectional view of a fiber used in the invention, in whichthe referential number 1 indicates the center point of cross section;

FIG. 3 is a set of sectional views of a conjugate fiber used in theinvention, in which (a) shows a cross section of concentric sheath-coreconfiguration, (b) shows a cross section of side-by-side configurationand (c) shows a cross section of islands-in-the-sea configuration,wherein the referential numbers 2 denotes a core portion, 3 denotes asheath portion, 4 denotes a first component and 5 denotes a secondcomponent;

FIG. 4 is a schematic view illustrating stretching gears;

FIG. 5 is a stress-strain curve obtained by a tensile test for compositenonwoven fabrics resulting in Examples; and

FIG. 6 is a stress-strain curve obtained by a tensile retest for thecomposite nonwoven fabrics illustrated in FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The extensible nonwoven fabric and the composite nonwoven fabricproduced by laminating the same according to the invention will bedescribed hereinbelow.

Extensible Nonwoven Fabric

(Induction Period of Strain-Induced Crystallization)

First, the “induction period of strain-induced crystallization” used inthe specification will be described. The induction period ofstrain-induced crystallization refers to a time from when a melt shearviscosity of a polymer starts to be measured at a constant measurementtemperature and a fixed shear strain rate till when the viscosity beginsto increase. Specifically, it is a time t_(i) illustrated in FIG. 1.That is, it denotes a time from the start of the measurement till whenthe melt shear viscosity that has been constant changes (increases).

Melt shear viscometers for use in the measurement of the melt shearviscosity include rotational rheometers and capillary rheometers. Theshear strain rate is preferably 3 rad/s or less in view of maintaining astable flow when the crystallization has occurred to some extent.

The flow field in a practical spinning is different from that in theabove measurement, and the strain rate is very high. The strain-inducedcrystallization of a polymer occurs when the total strain in the systemhas reached a certain level. Therefore, the induction period ofstrain-induced crystallization is in inverse proportion to the shearstrain rate, and the induction period of strain-induced crystallizationat a high shear strain rate can be estimated from the induction periodat a lower shear strain rate. Similarity between the flow field in thespinning and that in the above measurement is that polymer molecules areoriented by the flow. Therefore, it could be possible to estimate thephenomenon in the elongational flow filed in the practical spinningbased on the results obtained at a lower shear strain rate.

The induction period of strain-induced crystallization will be measuredat a temperature not lower than the static crystallization temperature,and preferably at between the static crystallization temperature and theequilibrium melting point. The measurement temperature is notparticularly limited as long as the induction periods of strain-inducedcrystallization of the polymers used can be compared at the temperature,that is, the difference in induction periods of strain-inducedcrystallization among the polymers can be distinct. Preferably, theinduction periods of strain-induced crystallization are compared at thehighest of the temperatures at which the resulting induction periods ofstrain-induced crystallization are comparable. The induction periods ofstrain-induced crystallization will be preferably different from eachother by 50 seconds or longer, and more preferably by 100 seconds orlonger. The greater the difference, the more remarkable the effect ofthe invention.

Whether or not the induction periods of strain-induced crystallizationwill differ from each other may be assumed based on the differences ofthe melt flow rates (MFR) and of the melting points measured under thesame conditions. Specifically, the polymers having different inductionperiods of strain-induced crystallization can be the followingcombinations (i) to (iii):

(i) Polymers having different MFR and different melting points;

(ii) Polymers having the same MFR and different melting points;

(iii) Polymers having different MFR and the same melting point.

Polymers with the same MFR and the same melting point have the sameinduction period of strain-induced crystallization.

<Olefin-Based Polymer>

The olefin-based polymers for use in the invention include α-olefinhomopolymers and copolymers. Preferably, the olefin-based polymers willbe ethylene or propylene homopolymers, or copolymers of propylene and atleast one α-olefin selected from α-olefins other than the propylene(hereinafter the “propylene copolymers”). The ethylene or propylenehomopolymers are more preferable. Particularly preferred are thepropylene homopolymers from the viewpoint of preventing fuzzing, andthus they are suitably used in disposable diapers.

The α-olefins other than propylene include ethylene and α-olefins of 4to 20 carbon atoms. Of these, ethylene and α-olefins of 4 to 8 carbonatoms are preferable, and ethylene, 1-butene, 1-pentene, 1-hexene,1-octene and 4-methyl-1-pentene are more preferable.

The “olefin-based polymers of the same kind” as used in the inventionwill be defined in the following (1) to (3). The descriptions in (1) and(2) explain the cases where the olefin-based polymers are singlepolymers, and the description in (3) is for the case where theolefin-based polymers are blends of two or more olefin-based polymers.

(1) Olefin-Based Homopolymers

As used herein, the “homopolymer” will refer to a polymer containing 90%or more of a main structural unit. That is, a polypropylene containingan ethylene unit in an amount of less than 10% may be considered as ahomopolypropylene. Accordingly, the expression “homopolymers of the samekind” means that they are, for example, all polyethylenes or allpolypropylenes that may contain a minor structural unit in an amount ofless than 10%.

(2) Olefin-Based Copolymers

The expression “copolymers of the same kind” means that all thecopolymers have the same combination of structural units and that theproportional difference of each corresponding structural units is lessthan 10% among the copolymers. For example, an ethylene/propylenecopolymer containing 80% propylene unit and 20% ethylene unit is of thesame kind as an ethylene/propylene copolymer in which the propylene unitis more than 70% and less than 90% and the ethylene unit is more than10% and less than 30%.

(3) Blends of Olefin-Based Polymers

In the invention, a blend comprising two or more polymers selected fromthe aforesaid homopolymers and copolymers may be used as an olefin-basedpolymer. These two or more polymers to be mixed together may be of thesame or different kind. As used in the invention, the expression“polymer blends of the same kind” means that all the polymer blends havethe same combination of polymer kinds and that the proportionaldifference of each corresponding polymers is less than 10% among thepolymer blends. For example, a polymer blend containing 80 wt %polypropylene and 20 wt % polyethylene is of the same kind as a polymerblend in which the polypropylene content is more than 70 wt % and lessthan 90 wt % and the polyethylene content is more than 10 wt % and lessthan 30 wt %.

The polyethylene for use in the invention will preferably range in MFR,as measured at 190° C. under a load of 2.16 kg in accordance with ASTMD-1238, from 1 to 100 g/10 min, more preferably from 5 to 90 g/10 min,and particularly preferably from 10 to 85 g/10 min. Also preferably, thepolyethylene will have an Mw/Mn ratio (Mw: weight-average molecularweight, Mn: number-average molecular weight) of 1.5 to 5. When the Mw/Mnratio is within the above range, the fiber will be beautifully spun andthe resultant fiber will have an excellent strength. As used herein, the“beautifully spinning” means that the resin can be extruded from aspinneret and drawn without filament breaking and the filament will notweld. In the invention, the weight-average molecular weight (Mw) and thenumber-average molecular weight (Mn) are the values in terms ofpolystyrene determined by a gel permeation chromatography (GPC) underthe conditions of:

Column: two TSKgel GMH6HT columns and two TSKgel GMH6-HTL columns

Column temperature: 140° C.

Mobile phase: o-dichlorobenzene (ODCB)

Flow rate: 1.0 mL/min

Sample concentration: 30 mg/20 mL ODCB

Injection amount: 500 μL

The analysis sample is prepared by dissolving 30 mg of a sample in 20 mLof o-dichlorobenzene by heating them at 145° C. for 2 hours, andfiltering the resultant solution through a sintered filter having 0.45μm pores.

The polypropylene generally has an equilibrium melting point of 185 to195° C. when its ethylene unit content is 0%. The polypropylene for usein the invention will preferably range in MFR, as measured at 230° C.under a load of 2.16 kg in accordance with ASTM D-1238, from 1 to 200g/10 min, more preferably from 5 to 120 g/10 min, and particularlypreferably from 10 to 100 g/10 min. Also preferably, the polypropylenewill have an Mw/Mn ratio (Mw: weight-average molecular weight, Mn:number-average molecular weight) of 1.5 to 5.0, and more preferably 1.5to 3.0. When the Mw/Mn ratio is within the above range, the fiber willbe beautifully spun and the resultant fiber will have an excellentstrength.

The at least two olefin-based polymers for use in the invention areprepared separately. Preferably, they are produced into pellets. Whentwo or more kinds of polymers are used in one olefin-based polymer, theyare preferably mixed together in a molten state and pelletized accordingto necessity.

<Additives>

In the invention, additives may be optionally used with the olefin-basedpolymers so long as the objects of the invention are not impaired. Theadditives include various stabilizers, such as heat stabilizers andweathering stabilizers, fillers, antistatic agents, hydrophilizingagents, slip agents, anti-blocking agents, anti-fogging agents,lubricants, dyes, pigments, natural oils, synthetic oils and waxes.

Exemplary stabilizers include anti-aging agents such as2,6-di-t-butyl-4-methylphenol (BHT); phenol-based antioxidants such astetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane,β-(3,5-di-t-butyl-4-hydroxyphenyl) propionic acid alkyl ester,2,2′-oxamidobis[ethyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)] propionate andIrganox 1010 (trade name, hindered phenol type antioxidant); fatty acidmetal salts such as zinc stearate, calcium stearate and calcium1,2-hydroxystearate; and fatty acid esters of polyvalent alcohols suchas glycerin monostearate, glycerin distearate, pentaerythritolmonostearate, pentaerythritol distearate and pentaerythritoltristearate. These stabilizers may be used singly or in combination oftwo or more kinds.

Exemplary fillers include silica, diatomaceous earth, alumina, titaniumoxide, magnesium oxide, pumice powder, pumice balloon, aluminumhydroxide, magnesium hydroxide, basic magnesium carbonate, dolomite,calcium sulfate, potassium titanate, barium sulfate, calcium sulfite,talc, clay, mica, asbestos, calcium silicate, montmorillonite,bentonite, graphite, aluminum powder and molybdenum sulfide.

Preferably, the additives will be used in a mixed condition with theolefin-based polymers. The additives may be mixed with one or more ofthe olefin-based polymers. The mixing method is not particularly limitedand may be a traditional process.

<Fiber>

The fiber for use in the invention comprises at least two olefin-basedpolymers as described hereinabove. These two or more olefin-basedpolymers are of the same kind and have different induction periods ofstrain-induced crystallization as measured at the same temperature andthe same shear strain rate. The fiber has substantially no crimps. By“having substantially no crimps”, it is meant that the crimps of thefiber constituting the nonwoven fabric do not influence theextensibility of the nonwoven fabric.

The fiber is a conjugate fiber and, as illustrated in FIG. 2, preferablyhas a cross section in which the polymer component in point (a) and thepolymer component in point (b) which is symmetric about the center pointare the same. As used herein, the “conjugate fiber” will refer to amonofilament in which there are at least two phases that have alength/diameter ratio appropriate to be called as a fiber phase. Here,the diameter will be considered as of the cross section of fiberregarded as a circle. That is, the conjugate fiber used in the inventionis a monofilament which contains at least two fiber phases comprisingthe olefin-based polymers that are of the same kind and have differentinduction periods of strain-induced crystallization.

The conjugate fiber may have a sheath-core configuration, a side-by-sideconfiguration or an islands-in-the-sea configuration across its crosssection. Specifically, the sheath-core conjugate fiber can take aconcentric configuration in which the circular core portion and thedoughnut-shaped sheath portion are arranged in concentric relation. Ofthe above configurations, the concentric sheath-core configuration ispreferable. These configurations across the cross section of conjugatefiber will be illustrated in FIG. 3, in which (a) shows a concentricsheath-core arrangement, (b) shows a side-by-side arrangement and (c)shows an islands-in-the-sea arrangement. In these configurations of theconjugate fiber, at least one component in every phase should be in afiber form. For example, when the aforesaid polymer blends haveconstituted fiber phases, at least one component of the blend polymershould have a fiber form in every phase and others form athree-dimensional islands-in-the-sea structure within the fiber phase.

Among at least two olefin-based polymers constituting the fiber, theolefin-based polymer having the earliest (shortest) induction period ofstrain-induced crystallization is preferably contained in an amount of 1to 70 wt %, more preferably 1 to 50 wt %, and particularly preferably 1to 30 wt % of the fiber. When the olefin-based polymer with the earliestinduction period of strain-induced crystallization is contained at above70 wt %, the fiber cannot be beautifully spun. In that the concentricsheath-core conjugate fiber is beautifully spun and the resultant fiberhas high extensibility, the core portion preferably comprises theolefin-based polymer having an earlier induction period ofstrain-induced crystallization.

<Nonwoven Fabric>

The extensible nonwoven fabric according to the invention contains theabove fiber. Preferably, the extensible nonwoven fabric is a spunbondednonwoven fabric.

The extensible nonwoven fabric preferably has a mass per unit area(basis weight) of 3 to 100 g/m², and more preferably 10 to 40 g/m².Having this basis weight, the extensible nonwoven fabric will beexcellent in softness, touch, conformability to the body, conformityduring body movements, drape, economical efficiency and see-throughproperties.

Preferably, the extensible nonwoven fabric will have an extensibility ofnot less than 70%, more preferably not less than 100%, even morepreferably not less than 150%, and particularly preferably not less than180% under a maximum load in the machine direction (MD) and/or in thecross machine direction (CD). Extensibility of less than 70% can causefracture during the processing such as drawing, resulting in anoticeable loss in fabric strength and fuzzing. Therefore, it will bedifficult to achieve satisfactory performances, such as good touch, whenused in disposable diapers and similar products. Particularly, when theextensible nonwoven fabric with the basis weight of 10 to 40 g/m² hasthe extensibility of usually not less than 70%, preferably not less than100%, more preferably not less than 150%, and particularly preferablynot less than 180%, it will exhibit very excellent practical propertiesincluding touch and body conformity.

Preferably, the extensible nonwoven fabric will have a fineness of 5.0denier or less. Having the fineness of not more than 5.0 denier, thenonwoven fabric will have excellent softness.

The extensible nonwoven fabric may be produced by a number of commonlyknown processes. For example, dry spinning, wet spinning, spunbondingand meltblowing may be employed. The spinning method may beappropriately selected depending on desired properties of the nonwovenfabric. The spunbonding method may be preferably used due to its highproductivity and because it can produce highly strong nonwoven fabrics.

Hereinbelow, the method of producing the extensible nonwoven fabric willbe described by reference to a production of spunbonded nonwoven fabricwhich contains concentric sheath-core conjugate fibers comprising twoolefin-based polymers. It should be understood that the productionmethod of the extensible nonwoven fabric is not limited to thefollowing.

First, two olefin-based polymers will be produced separately. Herein,the additive(s) may be added to one or both of the two olefin-basedpolymers when needed. The olefin-based polymers are molten in arespective extruder or like means such that the core portion comprisesone polymer and the sheath portion comprises another polymer. Then theolefin-based polymers are extruded through a spinneret with conjugatespinning nozzles designed to produce a desired concentric sheath-coreconfiguration. The concentric sheath-core conjugate continuous fiberthus spun is cooled with a cooling fluid, then stretched to apredetermined finesses by drawing air, and deposited on a collectingbelt in a predetermined thickness. The web is then subjected to anentanglement treatment, such as needle punching, water jetting orultrasonic sealing, or thermal bonding with a hot embossing roll. Thedesired spunbonded nonwoven fabric comprising the concentric sheath-coreconjugate fiber can be thus obtained. The hot embossing roll used in thethermal bonding may have an arbitrary embossing area percentage;preferably, the embossing area percentage will be 5 to 30%.

The extensible nonwoven fabric of the invention can be heat-embossed atlow temperatures. As a result, fuzzing will rarely take place and wideapplications including disposable diapers can be attained. Since heextensible nonwoven fabric of the invention can be embossed at a lowtemperature, it has an ability of reduction of energy costs in theproduction.

The extensible nonwoven fabric may be subjected to stretching by acommon procedure. Stretching (elongating) in the machine direction (MD)may be performed by passing the extensible nonwoven fabric through twoor more sets of nip rolls. In this stretching, each set of nip rollswill be operated faster than the previous set in the machine direction(MD). Further, gear stretching may be performed using stretching gearsas shown in FIG. 4.

Composite Nonwoven Fabric

The composite nonwoven fabric according to the invention comprises atleast one layer comprising the aforesaid extensible nonwoven fabric.Other layer (hereinafter the “other extensible layer”) than theextensible nonwoven fabric contained in the composite nonwoven fabric isnot particularly limited at least as long as it has extensibility.Preferably, the other extensible layer comprises an elastic polymerhaving both contraction and expansion properties.

The elastic polymers used include elastic materials having extensibilityand contractility. Vulcanized gums and thermoplastic elastomers aresuitable elastic materials. Particularly, thermoplastic elastomers arepreferable due to their excellent formability. The thermoplasticelastomers are high-molecular materials that show elastic properties asdo vulcanized rubbers at room temperature (which is due to the softsegments in the molecule) and that can be molded with a common moldingmachine at higher temperatures likewise with thermoplastic resins (whichis due to the hard segments in the molecule).

The thermoplastic elastomers usable in the invention include urethaneelastomers, styrene elastomers, polyester elastomers, olefin elastomersand polyamide elastomers.

The urethane elastomers are polyurethanes that are obtained by reactionof polyester or low molecular weight glycol with methylenebisphenylisocyanate or tolylene diisocyanate. Examples thereof include adducts,such as polyether polyurethanes, resulting from addition polymerizationof polyisocyanate to polylactone ester polyol in the presence ofshort-chain polyols; adducts, such as polyester polyurethanes, resultingfrom addition polymerization of polyisocyanate to polyol adipate formedfrom adipic acid and glycol, in the presence of short-chain polyols; andadducts obtained by addition polymerization of polyisocyanate topolytetramethylene glycol resulting from ring opening oftetrahydrofuran, in the presence of short chain polyols. These urethaneelastomers are commercially available under the trademarks of Resamine(Dainichiseika Color & Chemicals Mfg. Co., Ltd.), Miractolan (NipponPolyurethane Industry Co., Ltd.), Elastolan (BASF), Pandex and Desmopan(DIC-Bayer Polymer Ltd.), Estene (B.F. Goodrich) and Pellethane (DowChemical Company).

The styrene elastomers include styrene block copolymers, such as SEBS(styrene/(ethylene-butadiene)/styrene), SIS (styrene/isoprene/styrene),SEPS (styrene/(ethylene-propylene)/styrene) and SBS(styrene/butadiene/styrene). These styrene elastomers are commerciallyavailable under the trademarks of Kraton (Shell Chemicals), Cariflex TR(Shell Chemicals), Solprene (Phillips Petroleum Co.), Europrene SOL T(Enichem Elastomers), Tufprene (Asahi Kasei Corporation), Solprene T(Japan Elastomer Co., Ltd.), JSRTR (JSR Corporation), Denka STR (DenkiKagaku Kogyo K.K.), Quintac (Zeon Corporation), Kraton G (ShellChemicals), Tuftec (Asahi Kasei Corporation) and Septon (Kuraray Co.,Ltd.).

The polyester elastomers include those containing a hard segmentcomprising aromatic polyester and a soft segment comprisingnon-crystalline polyether or aliphatic polyester. Specific examplesinclude polybutylene terephthalate/polytetramethylene ether glycol blockcopolymers.

The olefin elastomers include ethylene/α-olefin random copolymers andthose obtained by copolymerizing a diene as a third component to therandom copolymers. Specific examples include those containing a hardsegment comprising polyolefin and a soft segment comprisingethylene/propylene random copolymer, ethylene/1-butene random copolymer,or ethylene/propylene/diene copolymer (EPDM) such asethylene/propylene/dicyclopentadiene copolymer orethylene/propylene/ethylidene norbornene copolymer. These olefinelastomers are commercially available under the trademarks of Tafmer(Mitsui Chemicals Inc.) and Milastomer (Mitsui Chemicals Inc.).

The polyamide elastomers include those containing a hard segmentcomprising nylon and a soft segment comprising polyester or polyol.Specific examples include Nylon 12/polytetramethylene glycol blockcopolymers.

Of these, the urethane, styrene and polyester elastomers are preferred.Particularly, the urethane and styrene elastomers are preferred in viewof excellent contraction and expansion properties.

The other extensible layer may be contained into various forms,including filament, net, film and foam. These layers can be produced bya common method.

The composite nonwoven fabric according to the invention can be obtainedby bonding the layer of the extensible nonwoven fabric and the otherextensible layer by a conventional method. The bonding methods includehot embossing, ultrasonic embossing, through hot-air bonding, needlepunching, and adhesive bonding.

The adhesives for use in the adhesive bonding include resin adhesivessuch as vinyl acetate adhesives and polyvinyl alcohol adhesives, andrubber adhesives such as styrene/butadiene adhesives, styrene/isopreneadhesives and urethane adhesives. Solvent adhesives obtained bydissolving the aforesaid adhesives in organic solvents, and aqueousemulsion adhesives obtained from the aforesaid adhesives are alsoemployable. Of these adhesives, the rubber hot melt adhesives, such asstyrene/butadiene adhesives and styrene/isoprene adhesives, arepreferably used since they do not deteriorate the texture.

The composite nonwoven fabric may be subjected to stretching by a commonprocedure likewise with the extensible nonwoven fabric.

Applications

The extensible nonwoven fabric and the composite nonwoven fabricaccording to the invention are excellent in extensibility, tensilestrength, fuzz resistance, surface abrasion resistance, formability andproductivity. Therefore, they can be used in wide industrialapplications including medical, hygiene and wrapping products. Inparticular, they can be suitably used in disposable diapers.

EXAMPLES

The present invention will be described by the following Examples, butit should be construed that the invention is in no way limited to theExamples. The measurement and comparison procedures for the inductionperiods of strain-induced crystallization are described below. Also, theprocedures in a tensile test and a fuzz resistance evaluation for thenonwoven fabrics are illustrated.

<Evaluation Procedures>

(1) Measurement of Induction Period of Strain-Induced Crystallization

The induction period of strain-induced crystallization was determined ata temperature between the equilibrium melting point and the staticcrystallization temperature of the polymer. The melt shear viscosity wasmeasured at a constant temperature and a fixed shear strain rate todetermine the induction period of strain-induced crystallization. Themeasurement was made first at around the equilibrium melting point, andwhen no increase in viscosity was observed within 7200 seconds from themeasurement initiation, the measurement temperature was lowered and themelt shear viscosity was measured again. This procedure was repeateduntil the induction period of strain-induced crystallization wasdetermined within 7200 seconds. The conditions in the measurement of themelt shear viscosity are given below.

Device: ARES Model produced by Rheometrics

Measurement mode: time sweep

Shear rate: 2.0 rad/s

Temperature: 130° C., 140° C., 150° C., 160° C., 170° C.

Tool: Cone plate (diameter: 25 mm)

Measurement environment: nitrogen atmosphere

(2) Comparison of SIC Induction Periods

The induction period of strain-induced crystallization of the polymerswere compared at the temperature determined as described below. First,the highest measurement temperature that the induction period ofstrain-induced crystallization is determined within 7200 seconds wasselected for each polymer (hereinafter the “selected temperature”).Thereafter, the induction periods of strain-induced crystallization ofthe polymers were compared at a comparison temperature which is thehighest temperature among all the selected temperatures of the polymersemployed.

(3) Measurement of Melt Flow Rate

The melt flow rate (MFR) was measured for the polymers in accordancewith ASTM D1238. The conditions are as follows:

Polypropylene: 230° C. under 2.16 kg load

Polyethylene: 190° C. under 2.16 kg load

(4) Measurement of Crystallization Temperature

The crystallization temperature was measured by a differential scanningcalorimeter (DSC). In the measurement, the polymer was heated to 200° C.at a rate of 10° C./min in a nitrogen atmosphere, maintained at thistemperature for 10 minutes, and cooled to 30° C. at a rate of 10°C./min. The temperature at exothermic peak obtained in the cooling wasdetermined as the crystallization temperature.

Based on the inventors' past experience in this field, the temperaturehigher than the crystalline temperature by 20° C. was determined as thestatic crystallization temperature.

(5) Tensile Test

Five specimens, each 25 mm in the machine direction (MD) and 2.5 mm inthe cross direction (CD), were extracted from the nonwoven fabric.Another five specimens, each 2.5 mm in the MD and 25 mm in the CD, wereextracted from the same nonwoven fabric. The former five specimens weresubjected to a tensile test using a constant extension tensile testerunder the conditions of chucks distance of 100 mm and a stress rate of100 mm/min. The maximum load in the machine direction, the extensibilityat the maximum load and the elongation at break (no load) were measuredfor the five specimens and the results were averaged. With respect tothe latter five specimens too, the maximum load in the cross direction,the extensibility at the maximum load and the elongation at break weremeasured in the tensile test and the results were averaged.

(6) Fuzz Resistance Measurement (Brushing Test)

The fuzz resistance was determined in accordance with JIS L1076. Threespecimens, each 25 mm in the MD and 20 mm in the CD, were extracted fromthe nonwoven fabric. The specimens were placed on a holder of a testerwith brush and sponge. In the test, a felt was used instead of the brushand sponge, and the specimens were rubbed therewith 200 times at a rateof 58 rpm. The rubbed specimens were visually observed and the fuzzresistance was evaluated based on the following criteria.

(Evaluation Criteria)

5: no fuzzing

4: little fuzzing

3: some fuzzing

2: noticeable fuzzing but no fracture

1: noticeable fuzzing and fracture

<Polypropylenes>

Polypropylenes (PP1 to PP5) used in Examples and Comparative Exampleshad the properties illustrated in Table 1.

TABLE 1 PP1 PP2 PP3 PP4 PP5 SIC induction period (sec) 170°C. >7200 >7200 >7200 >7200 >7200 160° C. >7200 >7200 >7200 >7200 >7200150° C. >7200 >7200 >7200 >7200 >7200 140° C. 279 319 399 >7200 >7200130° C. Not Not Not 719 1479 measured measured measured MFR (g/10 min)15 30 60 60 60 Melting point 162 162 162 142 138 (° C.) Mw/Mn 3.0 2.82.6 2.8 2.5 Ethylene unit 0 0 0 4 5 content (mol %) Crystallization 116116 116 101 94 temperature (° C.) Static 136 136 136 121 114crystallization temperature (° C.)

Example 1

PP1 and PP3 were melt spun into conjugate fibers which comprise the coreportion of PP1 and the sheath portion of PP3. The resultant conjugatefibers having the concentric sheath-core configuration with a weightratio of the core portion to the sheath portion of 10/90 (PP1/PP3) weredeposited on a collecting surface. The deposit was then heated andpressed with an embossing roll (embossing area percentage: 18%,embossing temperature: 120° C.) to give a spunbonded nonwoven fabrichaving a basis weight of 25 g/m² and a fiber fineness of 3.5 denier. Thespunbonded nonwoven fabric was tested to determine its properties. Theresults are shown in Table 2.

Example 2

A spunbonded nonwoven fabric was produced with the procedure illustratedin Example 1 except that PP4 was used in place of PP3 in the sheathportion and that the embossing temperature was changed from 120° C. to100° C. The spunbonded nonwoven fabric was tested to determine itsproperties. The results are shown in Table 2.

Example 3

A spunbonded nonwoven fabric was produced with the procedure illustratedin Example 1 except that PP5 was used in place of PP3 in the sheathportion and that the embossing temperature was changed from 120° C. to80° C. The spunbonded nonwoven fabric was tested to determine itsproperties. The results are shown in Table 2.

Example 4

A spunbonded nonwoven fabric was produced with the procedure illustratedin Example 3 except that PP2 was used in place of PP1 in the coreportion and that the embossing temperature was changed from 80° C. to100° C. The spunbonded nonwoven fabric was tested to determine itsproperties. The results are shown in Table 2.

Example 5

A spunbonded nonwoven fabric was produced with the procedure illustratedin Example 1 except that the core/sheath weight ratio was changed from10/90 to 20/80 and that the embossing temperature was changed from 120°C. to 100° C. The spunbonded nonwoven fabric was tested to determine itsproperties. The results are shown in Table 2.

Example 6

A spunbonded nonwoven fabric was produced with the procedure illustratedin Example 2 except that the core/sheath weight ratio was changed from10/90 to 20/80 and that the embossing temperature was changed from 100°C. to 80° C. The spunbonded nonwoven fabric was tested to determine itsproperties. The results are shown in Table 2.

Example 7

A spunbonded nonwoven fabric was produced with the procedure illustratedin Example 3 except that the core/sheath weight ratio was changed from10/90 to 20/80. The spunbonded nonwoven fabric was tested to determineits properties. The results are shown in Table 2.

Example 8

A spunbonded nonwoven fabric was produced with the procedure illustratedin Example 1 except that PP2 was used in place of PP1 in the coreportion and that the core/sheath weight ratio was changed from 10/90 to20/80. The spunbonded nonwoven fabric was tested to determine itsproperties. The results are shown in Table 2.

Example 9

A spunbonded nonwoven fabric was produced with the procedure illustratedin Example 4 except that the core/sheath weight ratio was changed from10/90 to 20/80. The spunbonded nonwoven fabric was tested to determineits properties. The results are shown in Table 3.

Example 10

A spunbonded nonwoven fabric was produced with the procedure illustratedin Example 4 except that the core/sheath weight ratio was changed from10/90 to 50/50 and that the embossing temperature was changed from 100°C. to 70° C. The spunbonded nonwoven fabric was tested to determine itsproperties. The results are shown in Table 3.

Example 11

A spunbonded nonwoven fabric was produced with the procedure illustratedin Example 9 except that PP3 was used in place of PP2 in the coreportion. The spunbonded nonwoven fabric was tested to determine itsproperties. The results are shown in Table 3.

Example 12

A spunbonded nonwoven fabric was produced with the procedure illustratedin Example 1 except that embossing temperature was changed from 120° C.to 100° C. and that the fiber fineness was altered from 3.5 denier to2.5 denier. The spunbonded nonwoven fabric was tested to determine itsproperties. The results are shown in Table 3.

Example 13

A spunbonded nonwoven fabric was produced with the procedure illustratedin Example 5 except that the fiber fineness was altered from 3.5 denierto 2.5 denier. The spunbonded nonwoven fabric was tested to determineits properties. The results are shown in Table 3.

Example 14

A spunbonded nonwoven fabric was produced with the procedure illustratedin Example 2 except that the fiber fineness was altered from 3.5 denierto 2.5 denier. The spunbonded nonwoven fabric was tested to determineits properties. The results are shown in Table 3.

Example 15

A spunbonded nonwoven fabric was produced with the procedure illustratedin Example 6 except that the fiber fineness was altered from 3.5 denierto 2.5 denier. The spunbonded nonwoven fabric was tested to determineits properties. The results are shown in Table 3.

Example 16

A spunbonded nonwoven fabric was produced with the procedure illustratedin Example 3 except that the fiber fineness was altered from 3.5 denierto 2.5 denier. The spunbonded nonwoven fabric was tested to determineits properties. The results are shown in Table 4.

Example 17

A spunbonded nonwoven fabric was produced with the procedure illustratedin Example 7 except that the fiber fineness was altered from 3.5 denierto 2.5 denier. The spunbonded nonwoven fabric was tested to determineits properties. The results are shown in Table 4.

Example 18

A spunbonded nonwoven fabric was produced with the procedure illustratedin Example 4 except that the fiber fineness was altered from 3.5 denierto 2.5 denier. The spunbonded nonwoven fabric was tested to determineits properties. The results are shown in Table 4.

Example 19

A spunbonded nonwoven fabric was produced with the procedure illustratedin Example 9 except that the fiber fineness was altered from 3.5 denierto 2.5 denier. The spunbonded nonwoven fabric was tested to determineits properties. The results are shown in Table 4.

Comparative Example 1

PP3 and a polyethylene (PE1) were used as the olefin-based polymers. Thepolyethylene (PE1) had MFR, as measured at 190° C. under a load of 2.16kg in accordance with ASTM D1238, of 60 g/10 min, a density of 0.93g/cm³ and a melting point of 115° C.

A spunbonded nonwoven fabric was produced with the procedure illustratedin Example 11 except that PE1 was used in place of PP5 in the sheathportion and that the embossing temperature was changed from 100° C. to110° C. The spunbonded nonwoven fabric was tested to determine itsproperties. The results are shown in Table 4.

Comparative Example 2

PP3 alone was melt spun and the monocomponent fiber was deposited on acollecting surface. The deposit was then heated and pressed with anembossing roll (embossing area percentage: 18%, embossing temperature:130° C.) to give a spunbonded nonwoven fabric having a basis weight of25 g/m² and a fiber fineness of 3.5 denier. The spunbonded nonwovenfabric was tested to determine its properties. The results are shown inTable 5.

Comparative Example 3

A spunbonded nonwoven fabric was produced with the procedure illustratedin Comparative Example 2 except that PP4 was used in place of PP3. Thespunbonded nonwoven fabric was tested to determine its properties. Theresults are shown in Table 5.

Comparative Example 4

A spunbonded nonwoven fabric was produced with the procedure illustratedin Comparative Example 2 except that the fiber fineness was altered from3.5 denier to 2.5 denier. The spunbonded nonwoven fabric was tested todetermine its properties. The results are shown in Table 5.

Comparative Example 5

A spunbonded nonwoven fabric was produced with the procedure illustratedin Comparative Example 2 except that the embossing temperature waschanged from 130° C. to 80° C. The spunbonded nonwoven fabric was testedto determine its properties. The results are shown in Table 5.

TABLE 2 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Core portion (A)Resin PP1 PP1 PP1 PP2 PP1 PP1 PP1 PP2 SIC induction period (140° C.)(sec) 279 279 279 319 279 279 279 319 MFR (g/10 min) 15 15 15 30 15 1515 30 Melting point (° C.) 162 162 162 162 162 162 162 162 Sheathportion (B) Resin PP3 PP4 PP5 PP5 PP3 PP4 PP5 PP3 SIC induction period(140° C.) (sec) 399 >7200 >7200 >7200 399 >7200 >7200 399 MFR (g/10 min)60 60 60 60 60 60 60 60 Melting point (° C.) 162 142 138 138 162 142 138162 Core/Sheath weight ratio (A/B) 10/90 10/90 10/90 10/90 20/80 20/8020/80 20/80 Embossing temperature (° C.) 120 100 80 100 100 80 80 120Fiber fineness (d) 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5 Basis weight (g/m²)25 25 25 25 25 25 25 25 Extensibility at maximum load (%) MD 191 201 177123 157 186 192 80 CD 161 177 163 124 92 156 140 60 Elongation at break(%) MD 199 221 187 132 167 201 202 93 CD 169 185 176 134 125 176 158 82Fuzz resistance 5 5 5 5 5 5 5 5

TABLE 3 Ex. 9 Ex. 10 Ex. 11 Ex. 12 Ex. 13 Ex. 14 Ex. 15 Core portion (A)Resin PP2 PP2 PP3 PP1 PP1 PP1 PP1 SIC induction period (140° C.) (sec)319 319 399 279 279 279 279 MFR (g/10 min) 30 30 60 15 15 15 15 Meltingpoint (° C.) 162 162 162 162 162 162 162 Sheath portion (B) Resin PP5PP5 PP5 PP3 PP3 PP4 PP4 SIC induction period (140° C.)(sec) >7200 >7200 >7200 399 399 >7200 >7200 MFR (g/10 min) 60 60 60 6060 60 60 Melting point (° C.) 138 138 138 162 162 142 142 Core/Sheathweight ratio (A/B) 20/80 50/50 20/80 10/90 20/80 10/90 20/80 Embossingtemperature (° C.) 100 70 100 100 100 100 80 Fiber fineness (d) 3.5 3.53.5 2.5 2.5 2.5 2.5 Basis weight (g/m²) 25 25 25 25 25 25 25Extensibility at maximum load (%) MD 123 81 95 149 141 174 170 CD 178 5089 103 101 140 143 Elongation at break (%) MD 131 128 102 167 171 183175 CD 192 112 108 127 135 158 159 Fuzz resistance 5 5 5 5 5 5 5

TABLE 4 Ex. 16 Ex. 17 Ex. 18 Ex. 19 Comp. Ex. 1 Core portion (A) ResinPP1 PP1 PP2 PP2 PP3 SIC induction period (140° C.) (sec) 279 279 319 319399 MFR (g/10 min) 15 15 30 30 60 Melting point (° C.) 162 162 162 162162 Sheath portion (B) Resin PP5 PP5 PP5 PP5 PE1 SIC induction period(140° C.) (sec) >7200 >7200 >7200 >7200 — MFR (g/10 min) 60 60 60 60 60(190° C.) Melting point (° C.) 138 138 138 138 115 Core/Sheath weightratio (A/B) 10/90 20/80 10/90 20/80 20/80 Embossing temperature (° C.)80 80 100 100 110 Fiber fineness (d) 2.5 2.5 2.5 2.5 3.5 Basis weight(g/m²) 25 25 25 25 25 Extensibility at maximum load (%) MD 164 129 116119 157 CD 138 188 160 144 157 Elongation at break (%) MD 173 142 123128 169 CD 154 197 169 155 172 Fuzz resistance 5 5 5 5 1

TABLE 5 Comp. Comp. Comp. Comp. Ex. 2 Ex. 3 Ex. 4 Ex. 5 Resin PP3 PP4PP3 PP3 SIC induction period 399 >7200 399 399 (140° C.) (sec) MFR (g/10min) 60 60 60 60 Melting point (° C.) 162 142 162 162 Embossingtemperature (° C.) 130 130 130 80 Fineness (d) 3.5 3.5 2.5 3.5 Basisweight (g/m²) 25 25 25 25 Extensibility at maximum MD 47 69 26 22 load(%) CD 39 55 35 29 Elongation at break (%) MD 61 75 50 72 CD 64 60 56 91Fuzz resistance 5 5 5 1

Example 20

PP1 and PP3 were melt spun into conjugate fibers which comprise the coreportion of PP1 and the sheath portion of PP3. The resultant conjugatefibers having the concentric sheath-core configuration with a weightratio of the core portion to the sheath portion of 10/90 (PP1/PP3) weredeposited on a collecting surface. Thereon, SEPS(styrene/(ethylene-propylene)/styrene) block copolymer (trade name: SEPS2002 available from Kuraray Co., Ltd.) was spread by a commonmeltblowing process to produce a laminate. Thereafter, PP1 and PP3 weremelt spun into a concentric sheath-core conjugate fibers, and theresultant fibers were deposited on the above-obtained laminate. Theconcentric sheath-core conjugate fibers had the core portion of PP1 andthe sheath portion of PP3 with a core/sheath weight ratio of 10/90. Theresultant laminate (web) was then heated and pressed with an embossingroll (embossing area percentage: 18%, embossing temperature: 120° C.) togive a spunbonded/meltblown/spunbonded nonwoven fabric having a basisweight of 130 g/m².

A 50 mm wide specimen was extracted from the nonwoven fabric. Thespecimen was elongated to 180% of its original length by means of atensile tester and thereafter relaxed to 0% elongation. Thestress-strain curve obtained in the test is shown in FIG. 5. Thereafter,the specimen was again elongated to 180% of its original length andthereafter relaxed to 0% elongation. The stress-strain curve obtained inthis second test is shown in FIG. 6. There ware no filament fracture orthe like in the spunbonded nonwoven fabric layer after the tensiletests. The fuzz resistance test resulted in the evaluation of 5.

INDUSTRIAL APPLICABILITY

The invention provides an extensible nonwoven fabric and a compositenonwoven fabric comprising the extensible nonwoven fabric, both beingexcellent in extensibility, tensile strength, fuzz resistance, surfaceabrasion resistance, formability and productivity. They can be used inwide industrial applications including medical, hygiene and wrappingproducts. In particular, they can be suitably used in disposable diapersdue to their comfortable touch attributed to excellent fuzz resistance.

1. An extensible nonwoven fabric which is a spunbonded nonwoven fabricthat comprises a fiber having substantially no crimps and comprising atleast two olefin-based polymers, said at least two olefin-based polymersbeing of the same kind and having a difference between induction periodsof strain-induced crystallization, as measured at the same temperatureand the same shear strain rate, of 100 seconds or longer, wherein amongthe at least two olefin polymers constituting the fiber, theolefin-based polymer having the earliest induction period ofstrain-induced crystallization is contained in an amount of 1 to 20 wt %of the fiber, and wherein the fiber is a conjugate fiber having aconcentric sheath-core configuration, in which the core resin has theearliest induction period of strain-induced crystallization.
 2. Theextensible nonwoven fabric according to claim 1, which has anextensibility at a maximum load of not less than 70% in the machinedirection (MD) and/or in the cross machine direction (CD).
 3. Theextensible nonwoven fabric according to claim 1, wherein theolefin-based polymer is a propylene-based polymer.
 4. A compositenonwoven fabric comprising at least one layer comprising the extensiblenonwoven fabric as described in claim
 1. 5. A disposable diapercomprising the extensible nonwoven fabric as described in claim 1.